For the dispersing of solids (e.g., fillers, dyes or pigments) in liquid media it is regular practice to make use of dispersants in order to achieve effective dispersing of the solids, to reduce the mechanical shear forces required for dispersing, and at the same time to realize very high degrees of filling. The dispersants assist the disruption of agglomerates. As surface-active materials they wet and/or cover the surface of the particles to be dispersed, and stabilize said particles against unwanted reagglomeration.
In the production of paints, varnishes, printing inks, and other coating materials, dispersants facilitate the incorporation of solids, such as fillers and pigments, which are important formulating ingredients and are essential determinants of the visual appearance and of the physicochemical properties of such systems. Optimum utilization requires firstly that these solids be distributed uniformly in the formulations and secondly that the state of distribution, once attained, is stabilized.
A host of different substances are nowadays used as dispersants for solids. In addition to simple low molecular mass compounds such as lecithin, fatty acids and their salts, and alkylphenol ethoxylates, more complex high molecular mass structures are used as dispersants. Amino-functional and amido-functional polymeric systems in particular find broad use here.
U.S. Pat. No. 4,224,212, EP-B-0 208 041, WO-A-00/24503, and WO-A-01/21298, for example, describe dispersants based on polyester-modified polyamines. DE-B-197 32 251 describes polyamine salts and their use as dispersants for pigments and fillers.
Use of these products as dispersing resins, however, also entails a multiplicity of drawbacks: when they are used in pigment pastes, high levels of the dispersing additives are frequently necessary; the achievable levels of pigmentation in the pastes are unsatisfactorily low; the stability of the pastes and hence their consistency of viscosity is inadequate; and flocculation and aggregation cannot always be avoided. In many instances the pastes lack consistency of hue after storage, and lack compatibility with diverse binders. The use of known dispersing additives in many cases also adversely affects the water resistance or light stability of coating materials, and additionally further stabilizes unwanted foam produced in the course of preparation and processing. Additionally, owing to a lack of compatibility of the dispersing resins in numerous letdown vehicles, gloss is often affected undesirably.
There exists, consequently, a growing demand for dispersants for solids that exhibit improved properties when compared with the state of the art. The requirement is for dispersants which will facilitate the dispersion of a multiplicity of solids in different media and provide stability by preventing reagglomeration of the said solids. In turn, the solid will be more uniformly dispersed throughout the liquid media and have better material processability, improved mechanical properties and improved opacity for pigments and dyes. With more effective dispersants, for example, it is possible to reduce the level of high-priced pigments used, without having to accept reductions in color strength.
Moreover, the viscosity characteristics of pastes, paints, varnishes, printing inks, and other coating materials comprising dyes, solids, such as fillers and/or pigments, are critically codetermined by the dispersant used. In particular, a demand exists for dispersants which have a low viscosity, as compared to untreated solids, in the liquid paints and varnishes and also retain such a viscosity. Lower viscosity mixtures have higher throughput and improved processability. Importantly, the use of viscosity-reducing dispersing resins will allow one to use increased loadings of fillers, dyes or pigments.